Very basic CAPTCHA challenge

For a browser based game (in PHP) we are having some issues with imacros bot scripts.

Without inconveniencing the regular player much like a standard CAPTCHA might if run too often) we were wondering if a simple flash solution might do the job.

Something like.. Load a flash graphic, and just have the user click on something that was placed in a random location. If done the game would continue...

I know flash can be decipherd by OCR, but it is unlikely our players would go to that effort. I guess it might be possible to do something like "Click on the Yellow Duck to continue" but I don't know that it would be needed.

At this point I am mostly interested in knowing if the concept is resonable, or if this could be bypassed by the average 7th grader...